<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
  </head>
  <body>
    <script>
    let uname = prompt('请输入用户名')
    let password = prompt('请输入密码')
    for(;;){
      if (uname === 'admin'&& password === '123456'){
        alert('登录成功')
        break
      }else {
        prompt('请输入用户名')
        prompt('请输入密码')
      }
    }
  </script>
  </body>
</html>